The data collected by wearable devices may be able to tell you much more than how many steps you've taken or hours you've slept. A new long-term study from researchers at the Stanford University School of Medicine suggests that fitness monitors, smart watches, and other wearable biosensors may be able to detect initial signs of illness before the wearer has noted any symptoms, according to a New Scientist report.

The results were published on January 12 in PLOS Biology. More than 40 individuals participated in the study and used wearable devices for up to two years. Researchers used the gadgets to track subjects’ pulse rates, skin temperature, and other measurements, and monitored when they deviated from normal baseline measurements. Sure enough, the researchers noticed that subjects exhibited an elevated heart rate up to three days before exhibiting signs of a cold or infection. Their skin temperature was sometimes higher, too.

“We think that if your heart rate and skin temperature are elevated for about two hours, there’s a strong chance you’re getting sick,” the study’s lead author, Michael Snyder, told New Scientist. (Snyder experienced the phenomenon first-hand when he received an early warning from a wearable that he had contracted Lyme disease during an excursion to rural New England.) Researchers also noticed that variations in heart rate patterns could distinguish between participants with insulin resistance (a risk factor for Type 2 diabetes) and healthy subjects, CBS News reports.

The research at this stage is still experimental, but Snyder and his colleagues are hoping to use what they've learned to build algorithms that let smart devices notify their wearers when they may be falling ill. Though the inevitable is still likely to occur, that way smart device owners will have been given fair warning—which means they can rest up and take care of themselves.

[h/t New Scientist]